Telecommunications network organizations started using optical fiber communication links just over 25 years ago. Since then, researchers have devised and developed a truly impressive collection of sophisticated passive and active optical components, transmission techniques that are unique to optical links, and software-based modeling tools for components, links, and networks. These developments enabled optical networks to deliver increasingly higher data rates over longer and longer distances for both terrestrial and transoceanic links.

The purpose of this chapter is to get an appreciation of this growth and to set the basis for understanding the material in the rest of the book. First we present the motivations for using optical communication, such as the physical differences and capacity advantages between electrical and optical signaling formats. Then we will review the evolution of optical fiber transmission systems, starting with the quest to create a viable optical fiber. This will lead us to present-day implementations. The chapter ends with an overview of the general concepts and issues of current transmission equipment, links, and networks. This includes the process of combining many independent wavelengths onto the same fiber, signal routing and switching, and standards for optical communications.